Such a type of conventional cylinder device with a force multiplier is disclosed in Patent Literature 1 (Japanese Patent Application Publication, Tokukai, No. 2007-268625 A). The conventional technology is configured as follows:
A clamping rod serving as an output rod is inserted in a housing so as to be movable vertically. A first piston for rod is inserted in an upper part of the housing, and is fixed to the clamping rod. A first lock chamber and a first release chamber are formed above and below the first piston, respectively. A second piston for force multiplication is inserted in a lower part of the housing, and is fitted on the clamping rod so as to be movable vertically. A second lock chamber and a second release chamber are formed above and below the second piston, respectively.
In a case where the clamping rod is subjected to lock driving, the first piston and the second piston are driven downward by supplying compressed air into the first lock chamber and the second lock chamber. This first causes the first piston to drive the clamping rod downward during a low-load stroke of the lock driving, and then causes the second piston to drive the clamping rod in a force-multiplying manner via a force multiplier during a high-load stroke that follows the low-load stroke.
Conventionally, the force multiplier includes: an engagement groove provided in a lower portion of the clamping rod; and a plurality of claw members swingably supported by the lower part of the housing. During the force multiplication driving, a tapered surface of the second piston, which has been driven downward, causes the claw members to swing radially inward, so that the claw members engage with the engagement groove.